1. Field of the Invention
The invention relates generally to illumination systems, and more particularly to a light array system for illumination of objects to be inspected.
2. Background of the Invention
Inspection of manufactured products helps to reduce the number of defective products introduced into the marketplace. The effectiveness of certain types of inspections, for example inspections of printed circuit boards or printed wiring boards (collectively xe2x80x9cPWBsxe2x80x9d), is often dependent upon the illumination systems and processes used to provide inspection lighting of the manufactured product during inspection.
This is especially true for automated inspection of PWBs using line scan camerasxe2x80x94the ability to identify, classify, and properly detect defects in the inspected PWBs is greatly affected by the lighting available on the subject PWB. Proper illumination allows for enhanced visibility of PWB manufacturing defects, including raw paste analysis (coverage and volume, missing/mis-aligned/damaged components, bent/missing/lifted leads, bridges and near bridges, alignment gauging, insufficient and excess solder, solder dewets, cold and fractured solder joints, etc.).
Several different illumination methodologies have been used for PWB inspection as well as other inspection tasks. These illumination techniques include highly diffuse (xe2x80x9ccloudy dayxe2x80x9d) illumination, direct illumination, re-directed illumination using fiber optics to distribute the source over a line, projected images of lines, ring lights, coaxial illumination, flood lights, as well as all of the above with some form of additional diffuser. Each of these methods proves inadequate when used for automated inspection of PWBs using a line scan camera for at least one or more of the following reasons: (1) inadequate overall light level; (2) excessive localized blooming or glinting (i.e., saturation of camera imaging elements due to excessive light); (3) insufficient coverage of light to fill shadows; and (4) image shiny, near vertical objects, such as leads.
For example, fixed angle single light sources cannot provide lighting to shadowed areas (such as shorter components surrounded by taller components or areas under vertical leads perpendicular to the scan direction). In order to get the light intensity required for inspection, these fixed angle light sources can also cause xe2x80x9cbloomingxe2x80x9d or very bright spots in the camera (due to the angle of reflection) that prevent inspection of that area because nothing could be discerned from the blooming area. In addition, because solder fillets are xe2x80x9cmound-shapedxe2x80x9d, regardless of the light angle variation, some reflection in a specular fashion back to the camera will occur. To a line scan camera, the shadow areas often look lack while the shiny or blooming areas look white and accurate detection of efects in these areas is difficult or impossible.
For the above reasons, there is a need for improving the automated inspection of devices such as PWBs.
The present invention provides an illumination system that substantially eliminates or reduces disadvantages and problems associated with previously developed illumination systems and methods used for automated inspection.
One embodiment of the invention relates to an illumination system for inspection of devices. The system includes a frame for positioning over an image area. A plurality of light source groups are coupled with the frame and are each configured to produce one or more wavelengths of light. Each light source group is configured to produce a wavelength of light which is not produced by another light source group.
In one embodiment of the illumination system, the light source groups are arranged such that each light source group includes the light sources producing a light beam with a central ray which is incident on the image area within a particular range of incident angles.
One embodiment of the system includes a plurality of light source groups coupled with the frame and configured to produce one or more wavelengths of light. Electronics control the wavelength of light produced by the light source groups such that each light source group produces a wavelength of light which is not produced by another light source group.
Another embodiment of the invention relates to a method for inspecting a device. The method includes positioning a frame over an image area. The frame includes a plurality of light source groups which are each configured to produce one or more wavelengths of light. Each light source is group configured to produce a wavelength of light which is not produced by another light source group. The method also includes generating a plurality of images. Each image is generated from the light produced by a different light source group.
Yet another embodiment of the invention relates to a method of illuminating a device to be inspected. The method includes positioning a frame over an image area and illuminating the image area from a plurality of light source groups attached to the frame. Each light source group is configured to produce a wavelength of light which is not produced by another light source group.